"Particularly the younger generation likes to think, 'I'll save more when I'm making more.' But whether you're making $50,000 a year or $200,000 a year, we all have challenges saving," says Kimmie Greene, money expert at Intuit and spokeswoman for Mint.com.

"Because oftentimes what happens is, when people make more," she says, "they end up spending more."

While the amount you need in savings is highly personal, and specific dollar amounts can be arbitrary, Greene offers a simple formula to help you figure out if you're setting aside enough money.

In your 20s: Aim to save 25% of your overall gross pay, Greene tells CNBC. "That 25% is the combination of 401(k) withholdings, matching funds from your employer and any cash savings that you have," she notes. "It can also include debt repayment.

"While this can sound super daunting today, if you're putting that money to work starting in your 20s, it's not as difficult as it sounds," says Greene.

She also notes that "life is anything but linear," and it's impossible to follow this formula to a tee. You may have to adjust accordingly and save more or less in any given year, depending on major life events, such as having a kid or buying a home.